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Key Findings

The State of the Air 2011 shows that the air quality in many places has improved during 2007-2009. Still, over 154 million people—just over one half the nation—suffer pollution levels that are too often dangerous to breathe. Despite great progress, air pollution lingers as a widespread and dangerous reality. It is important to note this progress, even as some seek to weaken the public health law that has improved the air we breathe since 1970, the Clean Air Act. Overall findings:

Roughly half the people (50.3%) in the United States live in counties that have unhealthful levels of either ozone or particle pollution. Almost 154.5 million Americans live in the 366 counties where they are exposed to unhealthful levels of air pollution in the form of either ozone or short-term or year-round levels of particles.

Roughly one in 17 people–more than 18.5 million in the United States–live in 10 counties with unhealthful levels of all three measures covered in the report: ozone and short-term and year-round particle pollution.

The strongest improvement came in reducing ozone smog levels across the nation. More than half of the country’s most-smog-polluted cities experienced their best year yet. All metro areas in the 25 cities most-polluted by ozone showed improvement over last year’s report. Still nearly half the people in the U.S. (48.2%) live in areas with unhealthful levels of ozone pollution.

All but two of the 25 cities most polluted by year-round levels of particle pollution (sometimes called soot) improved over last year’s report. Nineteen of those cities reported their best-ever particle pollution levels.

Success in reducing short-term particle pollution levels varied among metro areas. Twelve of the most polluted cities saw improvement compared to last year’s report, while 17 had worse problems with these spikes in particle levels.

The State of the Air 2011 report looks at levels of ozone and particle pollution found in official monitoring sites across the United States in 2007, 2008, and 2009. The report uses the most current quality-assured nationwide data available for these analyses.

For particle pollution, the report examines fine particulate matter (PM2.5) in two different ways: averaged year-round (annual average) and over short-term levels (24-hour). For both ozone and short-term particle pollution, the analysis uses a weighted average number of days that allows recognition of places with higher levels of pollution. For the year-round particle pollution rankings, the report uses averages calculated and reported by the U.S. Environmental Protection Agency. For comparison, the State of the Air 2010 report covered data from 2006, 2007 and 2008.1

A complete discussion of the sources of data and the methodology is included in Methodology.

FACT: Two cities—Honolulu, HI and Santa Fe, NM—ranked among the cleanest in all three air pollution categories covered in State of the Air.